I had just finished upgrading my base system by installing a cleansweep and 6 channel amp when I stupidly mixed up the head unit feed to the left rear that should have gone to the clean-sweep with the output left rear from my amp. I turned the system on and there was a short high-pitched noise then nothing.

I have just disconnected the head unit outputs to see if there is any sign of life. Iím not sure if this is the right way to measure the outputs but with a multi-meter set to AC there is approx. 40mV from the right channel front and rear and about 20mV from the front left and nothing from the left rear. I also connect a speaker to see if the audio could be heard. The right channel could but it was vey crackly and faint. The left channel could not be heard.

Have I wrecked my head-unit or something worse. Any help greatly appreciated or recommendations for a car hifi repairer.